Byssinosis or "Brown-lung" disease afflicts over one-half million textile workers in the United States of America. The main cause of this disease is believed to be the fine cotton dust of organic origin, most of which comes from the small dry, leaf-like appendages to the boll called bracts. All commercial cotton varieties have persistant bracts which adhere to the seed cotton as it matures. The mechanical harvesting operation shatters the brittle bracts which are mixed with the seed cotton, and upon ginning, becomes a major constituent of organic dust in the lint cotton. Water extracts of dried bracts are biologically active, and are known to cause byssinotic symptoms in humans, while water extracts of other cotton plant parts are asymptomatic. A type of hexaploid cotton that drops its bracts before the bolls opens has been developed in Arizona. This trait, called caducous bracts, is being transferred to tetraploid cotton cultivars in a breeding program. The transfer of caducous bract to cotton cultivars involves hybridization, back cross breeding, and selfing of plants with different chromosome numbers.